Summary.Creatine is
used in muscle cells to store energy for sprinting and explosive
exercise. Athletes can increase the amount of creatine in muscle by
taking creatine supplements. Although some studies report no
ergogenic effect, most indicate that creatine supplementation (e.g.
20 g per day for 5 to 7 days) increases sprint performance by 1-5%
and work performed in repeated sprints by up to 15%. These ergogenic
effects appear to be related to the extent of uptake of creatine into
muscle. Creatine supplementation for a month or two during training
has been reported to promote further gains in sprint performance
(5-8%), as well as gains in strength (5-15%) and lean body mass
(1-3%). The only known side effect is increased body weight. More
research is needed on individual differences in the response to
creatine, periodic or cyclical use of creatine, side effects, and
long-term effects on endurance.Reviewers' comments

Introduction

Creatine is an amino acid, like the building blocks that make up
proteins. Creatine in the form of phosphocreatine (creatine
phosphate) is an important store of energy in muscle cells. During
intense exercise lasting around half a minute, phosphocreatine is
broken down to creatine and phosphate, and the energy released is
used to regenerate the primary source of energy, adenosine
triphosphate (ATP). Output power drops as phosphocreatine becomes
depleted, because ATP cannot be regenerated fast enough to meet the
demand of the exercise. It follows that a bigger store of
phosphocreatine in muscle should reduce fatigue during sprinting.
Extra creatine in the muscle may also increase the rate of
regeneration of phosphocreatine following sprints, which should mean
less fatigue with repeated bursts of activity in training or in many
sport competitions.

So much for the theory, but can you get a bigger store of creatine
and phosphocreatine in muscle? Yes, and it does enhance sprint
performance, especially repeated sprints. Extra creatine is therefore
ergogenic, because it may help generate more power output during
intense exercise. In addition, long term creatine supplementation
produces greater gains in strength and sprint performance and may
increase lean body mass. In this article I'll summarize the evidence
for and against these claims. I'll draw on about 42 refereed research
papers and four academic reviews to make conclusions regarding the
ergogenic value of creatine supplementation. In addition, I'll
provide 25 references to studies published in abstract form, which
report the most recent preliminary findings on creatine
supplementation.

Effects of Creatine
Supplements on Muscle Creatine, Phosphocreatine, and ATP

The daily turnover of creatine is about 2 g for a 70 kg person.
About half of the daily needs of creatine are provided by the body
synthesizing creatine from amino acids. The remaining daily need of
creatine is obtained from the diet. Meat or fish are the best natural
sources. For example, there is about 1 g of creatine in 250 g (half a
pound) of raw meat. Dietary supplementation with synthetic creatine
is the primary way athletes "load" the muscle with creatine. Daily
doses of 20 g of creatine for 5-7 days usually increase the total
creatine content in muscle by 10-25%. About one-third of the extra
creatine in muscle is in the form of phosphocreatine
(Harris, 1992; Balsom
et al., 1995).

Extra creatine in muscle does not appear to increase the resting
concentration of ATP, but it appears to help maintain ATP
concentrations during a single maximal effort sprint. It mayalso enhance the rate of ATP and phosphocreatine resynthesis
following intense exercise (Greenhaff et
al., 1993a; Balsom et al., 1995;
Casey et al., 1996).

There is some evidence that not all subjects respond to creatine
supplementation. For example, one study reported that subjects who
experienced less of a change in resting muscle creatine (<20
mmol/kg dry mass) did not appear to benefit from creatine
supplementation (Greenhaff et al.,
1994). However, more recent studies indicate that taking creatine
with large amounts of glucose increases muscle creatine content by
10% more than when creatine is taken alone
(Green et al., 1996a;
Green et al., 1996b). Consequently,
ingesting creatine with glucose may increase its ergogenic effect.

Effects on
Performance

Researchers first investigated the ergogenic effects of short-term
creatine loading. In a typical study, a creatine dose of 5 g is given
four times a day for five to seven days to ensure that muscle
creatine increases. A control group is given a placebo (glucose or
some other relatively inert substance) in a double-blind manner
(neither the athletes nor the researchers doing the testing know who
gets what until after the tests are performed). Most studies have
shown that speed or power output in sprints--all-out bursts of
activity lasting a few seconds to several minutes--is enhanced,
typically by 5-8%. Repetitive sprint performance is also enhanced
when the rests between sprints don't allow full recovery. In this
case, total work output can be increased by 5-15%. There is also
evidence that work performed during sets of multiple repetition
strength tests may be enhanced by creatine supplementation, typically
by 5-15%. In addition, one-repetition maximum strength and
vertical-jump performance may also be increased with creatine
supplementation, typically by 5-10%. The improvement in exercise
performance has been correlated with the degree in which creatine is
stored in the muscle following creatine supplementation, particularly
in Type II muscle fibers (Casey et al.,
1996).

Researchers have now turned their attention to longer-term
creatine supplementation. In these studies, a week of creatine
loading of up to 25 g per day is followed by up to three months of
maintenance with reduced or similar dosages (2-25 g per day).
Training continues as usual in a group given creatine and in a
control group given a placebo. Greater gains are now seen in
performance of single-effort sprints, repeated sprints, and strength
(5-15%).

Table 1 at the end of this article lists the
references to positive effects of creatine on performance.
Theoretically, creatine may affect performance through one or more of
the following mechanisms (Table 2): an increase
in concentrations of creatine and phosphocreatine in resting muscle
cells; an increased rate of resynthesis of phosphocreatine between
bouts of activity; enhanced metabolic efficiency (lower production of
lactate, ammonia, and/or hypoxanthine); and enhanced adaptations
through higher training loads. Creatine supplementation during
training may also promote greater gains in lean body mass (see Body
Composition below).

Not all studies have reported ergogenic benefit of creatine
supplementation (Table 3). In this regard, a
number of equally well-controlled studies indicate that creatine
supplementation does not enhance: single or repetitive sprint
performance; work performed during sets of maximal effort muscle
contractions; maximal strength; or, submaximal endurance exercise.
What's more, one study reported that endurance running speed was
slower, possibly because of an increase in body mass
(Balsom et al., 1993b).

In analysis of these studies, creatine supplementation appears to
be less effective in the following situations: when less than 20 g
per day was used for 5 days or less; when low doses (2-3 g per day)
were used without an initial high-dose loading period; in crossover
studies with insufficient time (less than 5 weeks) to allow washout
of the creatine; in studies with relatively small numbers of
subjects; and when repeated sprints were performed with very short or
very long recovery periods between sprints. It is also possible that
subject variability in response to creatine supplementation may
account for the lack of ergogenic benefit reported in these studies.
In addition, there have been reports that caffeine may negate the
benefit of creatine supplementation
(Vandenberghe et al., 1996).
Consequently, although most studies indicate that creatine
supplementation may improve performance, creatine supplementation may
not provide ergogenic value for everyone.

Body Composition

Although some studies have found no effect, most indicate that
short-term creatine supplementation increases total body mass, by 0.7
to 1.6 kg. With longer use, gains of up to 3 kg more than in matched
control groups have been reported (see Table 4
at the end of this article for references). For example,
Kreider et al.(1998) reported that 28 days of
creatine supplementation (16 g per day) resulted in a 1.1 kg greater
gain in lean body mass in college football players undergoing
off-season resistance/agility training. In addition,
Vandenberghe et al. (1997) reported
that untrained females ingesting creatine (20 g per day for 4 days
followed by 5 g per day for 66 days) during resistance training
observed significantly greater gains in lean body mass (1.0 kg) than
subjects ingesting a placebo during training. The gains in lean body
mass were maintained while ingesting creatine (5 g per day) during a
10-week period of detraining and in the four weeks after
supplementation stopped.

Findings like these suggest that creatine supplementation may
promote gains in lean body mass during training, but we don't yet
understand how it works. The two prevailing theories are that
creatine supplementation promotes either water retention or protein
synthesis. More research is needed before we can be certain about the
contribution each of these processes makes to the weight gain.

Side Effects

In studies of preoperative and post-operative patients, untrained
subjects, and elite athletes, and with dosages of 1.5 to 25 g per day
for up to a year, the only side effect has been weight gain
(Balsom, Soderlund & Ekblom, 1994). Even
so, concern about possible side effects has been mentioned in lay
publications and mailing lists. Before discussing these possible side
effects, it should be noted that they emanate from unsubstantiated
anecdotal reports and may be unrelated to creatine supplementation.
We must be careful to base comments regarding side effects of
creatine supplementation on factual evidence, not speculation. But we
must also understand that few studies have directly investigated any
side effects of creatine supplementation. Consequently, discussion
about possible side effects is warranted.

Anecdotal reports from some athletic trainers and coaches suggest
that creatine supplementation may promote a greater incidence of
muscle strains or pulls. Theoretically, the gains in strength and
body mass may place additional stress on bone, joints and ligaments.
Yet no study has documented an increased rate of injury following
creatine supplementation, even though many of these studies evaluated
highly trained athletes during heavy training periods. Athletes
apparently adapt to the increase in strength, which is modest and
gradual.

There have been some anecdotal claims that athletes training hard
in hot or humid conditions experience severe muscle cramps when
taking creatine, and the cramps have been attributed to overheating
and./or changes in the amount of water or salts in muscle. But no
study has reported that creatine supplementation causes any cramping,
dehydration, or changes in salt concentrations, even though some
studies have evaluated highly trained athletes undergoing intense
training in hot/humid environments. In my experience with athletes
training in the heat (e.g., during 2-a-day football practice in
autumn), cramping is related to muscular fatigue and dehydration
while exercising in the heat. It is not related to creatine
supplementation. Nevertheless, athletes taking creatine while
training in hot and humid environments should be aware of this
possible side effect and take additional precautions to prevent
dehydration.

Some concern has been raised regarding the effects of creatine
supplementation on kidney function. The body seems to be able to
dispose of the extra creatine without any problem
(Poortmans et al., 1997). The extra creatine
is eliminated mainly in the urine as creatine, with small amounts
broken down and excreted as creatinine or urea. No study has shown
that creatine supplementation results in clinically significant
increases in liver damage or impaired liver function.

It has also been suggested that creatine supplementation could
suppress the body's own creatine synthesis. Studies have reported
that it takes about four weeks after cessation of creatine
supplementation for muscle creatine
(Vandenberghe et al., 1997) and
phosphocreatine (Febbraio et al., 1995)
content to return to normal. It is unclear whether muscle the content
falls below normal thereafter.Although more research is
needed, there is no evidence that creatine supplementation causes a
long-term suppression of creatine synthesis when supplementation
stops (Balsom, Soderlund & Ekblom, 1994;
Hultman et al., 1996).

Does creatine supplementation have undiscovered long-term side
effects? Trials lasting more than a year have not been performed, but
creatine has been used as a nutritional supplement for over 10 years.
Although long-term side effects cannot discounted, no significant
short-term side effects other than weight gain have been reported. In
addition, I am not aware of any significant medical complications
that have been linked to creatine supplementation. Furthermore,
creatine and phosphocreatine have been used medically to reduce
muscle wasting after surgery and to improve heart function and
exercise capacity in people with ischemic heart disease
(Pauletto & Strumia, 1996;
Gordon et al., 1995). Creatine supplementation
may even reduce the risk of heart disease by improving blood lipids
(Earnest, Almada & Mitchell, 1996;
Kreider et al., 1998). On the basis of the
available research, I consider creatine supplementation to be a
medically safe practice when taken at dosages described in the
literature.

Determining whether creatine supplementation has any short- or
long-term side effects is an area receiving additional research
attention. If there are side effects from long-term creatine
supplementation, an important issue will be the liability of coaches,
trainers, universities, and athletic governing bodies who provide
creatine to their athletes. Anyone advising athletes to take creatine
should make it clear that side effects from long-term use cannot be
completely ruled out, and that the athletes do not have to take the
supplements. It would be wise to have a formal policy for dosages to
reduce the chances of athletes taking excessive amounts.

Ethics

Creatine supplementation is not banned, but is a nutritional
practice that enhances performance nevertheless unethical? Anyone
pondering this question should consider that creatine supplementation
is a practice similar to carbohydrate loading, which is well
accepted. Some are also concerned that creatine supplementation could
cause a carryover effect, whereby athletes who have learned to take
creatine are more likely to use dangerous or banned substances.
Proper education among athletes, coaches, and trainers regarding
acceptable and unacceptable nutritional practices is probably the
best way to reduce any carryover.

How to Use Creatine

A typical loading regime for a 70-kg athlete is a 5-g dose four
times a day for a week. Thereafter the dose can be reduced to 2 to 5
g per day in order to maintain elevated creatine content. This
supplementation protocol will increase intramuscular creatine and
phosphocreatine content and enhance high intensity exercise
performance. There is now some evidence that taking glucose (100 g)
with the creatine (5 to 7 g) increases the uptake of creatine into
muscle (Green et al., 1996a;
Green et al., 1996b). Consequently, I
recommend that athletes take creatine with carbohydrate (e.g. with
grape juice) or ingest commercially available creatine supplements
that combine creatine with glucose. For athletes wanting to promote
additional gains in lean body mass, I recommend 15 to 25 g per day
for 1 to 3 months. Although many athletes cycle on or off creatine,
no study has determined whether this practice promotes greater gains
in fat free mass or performance than continuous use. More research is
needed here.

Creatine supplements are good value. Creatine is now being sold
for as little as US$30 per kg, or about $0.60 per day when taking 20
g per day. Popular sports drinks are more expensive.

Prevost, M., Nelson, A., Morris, G. (1997).
The effects of creatine supplementation on total work output and
metabolism during high-intensity intermittent exercise. Research
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Schneider, D., McDonough, P., Fadel, P.,
Berwick, J. (1997). Creatine supplementation and the total work
performed during 15-s and 1-min bouts of maximal cycling. Australian
Journal of Science in Medicine and Sport, 29, 65-68.